1 Introduction - Freie Universität · PDF fileOODBMS ⇒Object-Relational systems...

1 Introduction1 Introduction

1.1 Databases vs. files1.2 Basic concepts and terminology1.3 Brief history of databases1.4 Architectures & systems1.5 Technical Challenges1.6 DB lifecycle

References: Kemper / Eickler chap. 1, Elmasri / Navathe chap 1+2,and "Intro" of most DB books

01-DBS-Intro-2© HS-2010

1.1 Databases Systems versus File Based Processing

ExampleAdministration of courses, lecturers, rooms…

in a university ... KVV ;)

Typical operations:• "Find all my courses in summer term 2010"• "Find a room with capacity >20 Friday 8 am"• "Calculate mean number of courses for the

students"

Typically interactive and batch applications


Why Database systems?

Application program

Files

Reading and Writing Random Access Filesin Java (taken from Java API)

readpublic int read(byte[] b, int off, int len) throws IOException

Reads up to len bytes of data from this file into an array of bytes.This method blocks until at least one byte of input is available. Although RandomAccessFilenot a subclass of InputStream, this method behaves in the exactly the same way as theInputStream.read(byte[], int, int) method of InputStream. Parameters:b - the buffer into which the data is read.off - the start offset of the data.len - the maximum number of bytes read.

Returns:the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.

Throws:IOException - if an I/O error occurs.

More than 30 low level operations


AbstractionAbstraction

What is an appropriate language to manipulate data?

SELECT c.titel, c.hoursFROM Courses c, Lecturers eWHERE c.lecturer = e.id AND e.name = "HS"

AND c.sem = "SoSe2010" .

titel hours

DBS 5

TAS 4

...

Result: a table with 2 colums


Relational database Systems:

Definition and manipulation of data tables


File system versus DBSFile system versus DBS

Why database systems?

DBS provide an abstraction from the physical representation of data and from the implementation of operations (on data)

Aprog

Data base

High Level interface

AProgAProg

DBMS

SELECT name, semFROM RegisteredWHERE subject = 'Informatik'AND sem >= 4;


Files versus Database: differencesFiles versus Database: differences

– Application oriented read/write interface, high level access

– Database has it’s own data description (!) - the schema

– More secure access– Concurrent access to data– Fault tolerance

Nonfunctional characteristics


1.2 Basic Concepts and Terminology1.2 Basic Concepts and Terminology

1.2.1 Data independence

• Guiding principle: introduce levels of abstraction • Application program should be independent of physical

organization of datae.g. hash, B-Tree or sequential access to records should be transparent to the program (ignoring performance impacts)

Important term!

Def.: Physical Data independence

Application programs are not compromised when storage structure is changed


Basic AbstractionsBasic AbstractionsData Independence (cont)

ExampleSuppose participation in exams has to be introduced for each student in the university database

Goal: existing application programs should not need to be changed, except when logically necessary. (e.g. grades for exam presupposes partipation)

Def.: Logical data independence Application programs are not compromised by changes of the schema (if possible)


33--SchemaSchema--ArchitectureArchitecture

ANSI/X3/SPARC Architectural Model“separate physical aspects from logical data structuring

from individual user (application) views of the data”

Storage model hidden from applications

Physical layer

Conceptual layer

Storage and data model independent definitionof all data in the database.Sometimes called logical layer

External viewExternal view External view

Different applications have differentviews of storage and data model


How to specify a database?How to specify a database?

Important terms!

+name+matr_nr

Student+title+course_Nr

Course+attends

*

+

*

Conceptual modelDescribes high-level concepts in DB design models subset of real world.

Entity relationship model,(or UML: Universal Modelling Language)

CREATE TABLE student(name CHAR(..),MatrNr NUMBER,....)

Logical Data Model (DM)

e.g.

Search Tree

CREATE INDEX …

Physical (data) modelDeclarative ("logical") description of implementation schema

e.g.

Search Tree

CREATE INDEX …

Physical (data) modelDeclarative ("logical") description of implementation schema


Def.: Database schema:Formal description of some part of reality in terms of the data model (e.g. tables)

Schema defined on different levels: logical, physical, external

Schema: - specifies content of database on a type level,- in most cases: schema separate from data

"schema is first class object"- may be changed over time, but basically

static.- does not exist for files (hidden in program)


Def.: DatabaseSet of data objects conforming to a given database schema

Database: dynamic, time variantDB schema: basically static.

Important aspect: Primitives for

- schema specification- database operations

⇒ Data Model


1.2.2 Data models1.2.2 Data models

Most important data model today: Relations (tables) and SQL (or relational algebra)

Def.: Data Model is a language - for defining the schema (Data Definition Language DDL)

- for accessing and updating the DB(Data Manipulation Language DML)

Name phoneFName title

KunzHinz

3310133700

BobCathy

ProfDr.

schema

data: tables (set of rows)

Important term!


TheThe Relational Relational ModelModel

1970: Relational model [E.F. Codd: The Relational Data Model] -> reader

since 1980: RDBMS everywhere

Author

Name Email

HuntKatzMaus

[email protected]@...piep@...

FName

TinaAnnaCarl

Lecturer

Name phone

KunzHinz

3310133700

FName

BobCathy

title

ProfDr.

Course

Lecturer

HinzKatzHinz

Title

DBSCompilerSeminar

room

050305

....• All data represented

as tables,

• Schema ("Metadata") separate from data

Table name


Legacy data models (1)Legacy data models (1)

Hierarchical data model: hierarchies of record types

Still in use: IMS (Information Management System), a mainframe oldie.

customer

account

accRecord

A bank customer has one or more accounts, für each account,there are 0 or more accounting records

Kunz

198003 198435

+100€ -22€ +112€ +720€

schema data


Legacy data model (2)Legacy data model (2)

Network data model (“CODASYL”) : graph like data structures (see reader

SUPPLIER

PART

SchemaInstances

Example by Codd / Date, ACM SIGFIDET 1974


OtherOther datadata modelsmodels (1): XML (1): XML Pre-XML representation of data:

XML representation of the same data:

“PO-1234”,”CUST001”,”X9876”,”2”,”14.98”

Elements

<?xml version="1.0"?><PURCHASE_ORDER>

<PO_NUM> PO-1234 </PO_NUM><CUST_ID> CUST001 </CUST_ID>

<ITEM ItemNum ="x9876">

< QUNTY > 2 </ QUNTY >

<PRICE> 14.53 </PRICE>

</ITEM></PURCHASE_ORDER>

Attribute

Prologue


XML exampleXML example

Graphical representation of XML data

XML documents- tree structured - data and metadata in the same document

(as opposed to RDBS)

PO_NUM

PURCHASE_ORDER

Cust:_ID

QUNTYPO-1234 CUST001

2

{ ItemNum=X9876 }ITEM

PRICE

14.53

For those who donot know what XMLis: learn the basicshere.


Other Data models (2) Other Data models (2)

• RDF (Ressource description Framework)

• Object oriented (data) model? ... try to define.

• There is a set of Nodes (call it N). • There is a subset of N known as the PropertyTypes (call it P). • There is a set of 3-tuples called T, whose elements are

informally known as properties. The first item of each tuple is an element of P, the second item is an element of N and the third item is either an element of N or an atomic value (e.g. aUnicode string).

(Core Data Model of RDF, see http://www.w3.org/TR/WD-rdf-syntax-971002/ )


Other Data Models (3)Other Data Models (3)

Lightweight database systems– Key value stores ("schema less DBS")

– basic ideas:very simple schema language ("key:value"), very efficient access by key,offload most correctness guarantees to application.

Example (couchDB):{ "_id":"biking","_rev":"AE19EBC7654","title":"Biking",

"body":"My biggest hobby is mountainbiking. The other day...",

"date":"2009/01/30 18:04:11" }


Data modelData model

Caveat: – Data Model is a language.– Data Model is not the result of modeling some reality– This process is called data modeling– The result is the DB schema

Relational Data model:

~"Use tables to represent your data"

+name+matr_nr

Student+title+course_Nr

Course+attends

*

+

*

HinzKatzHinz

DBSCompilerSeminar

050305

Data model Schema (conceptual)

Database

...


1.2.3 Data base languages1.2.3 Data base languages

Conceptual level

External level (view)Data Definition (DDL) and Manipulation Language(DML)• Define logical data

structures (schema)• Query database

Data Administration Language• Define access path• Adjust tuning and otherparameters

Different language levels for relational (tabular) DBSall covered by SQL (Structured Query Language)

Physical level


SQL and Programming languagesSQL and Programming languages

Programming Languages– SQL is an interactive language– Most applications don’t allow users to use SQL

directly but have their own GUI (e.g. a forms based web interface )

– How do these applications talk to the DBS?

Embedded SQLDBS define an Application Programming Interface

(API) which is basically a standardized interface for calling the DBS from a program with the SQL-command to be executed and for transferring the result data.

Most popular: Embedded SQL / C and JDBC (Java)


1.3 History1.3 History at a at a glanceglance

• Business Data Processing as the driving force for DBS development

• ~ 1965 File system approach to data management leads to chaos.

• What are the right abstractions? ⇒ data model• 1970: Tables!

(Codd's seminal paper)• 1973: Research prototypes for Relational DBS,

Transactions• 1980: RDBMS everywhere,

Distributed DBS


History (cont) History (cont)

• 1990: Object orientation ⇒ OO data model and OODBMS ⇒ Object-Relational systems

• 1995: Wide scale distribution, WEB

• 1997: Semistructured data, Image DB, ... , XML / DB

• 2000++ Mobility and DBMS• 2005++ Unstructures Data – e.g. text. Querying text???

• Automated Object-relational mapping: only objects in the program, don’t care about relations


1.4 Architectures and Systems1.4 Architectures and Systems

Legacy systemsInformation Mangement Systems (IMS), hierarchical systems by IBMUniversal Data Store (UDS) , network system by Siemens

The dominating Relational DBMSOracle PostgresMySQLSQL-Server / MicrosoftSybaseDB2 / IBM, InformixAdabas (Software AG)personal, low cost desktop DBS: MSAccessJava "persistence" related DBS: Derby, ...


Integrated systemsIntegrated systems

More and more integration with application software, e.g. SAP R3 uses Oracle (mostly) behind the curtains

Corba-client

Java-client …….

…

Business Framework (objects, rules)

Component e.g. Controlling

Component e.g. Financial Accounting

Database

ERP system(EnterpriseRessourcePlanning)


MainframeMainframe

• Mainframe architecture

– Transaction monitor queues requests, schedules application programs (usually simple application logic)

Still in use today, e.g. flight reservation systemsvery efficient, but expensive hardware

Transaction-monitor

Applications

DBSOperating system

Terminals...

typically "big iron"(" 'ne richtig

große Maschine")


22--tier Architecturetier Architecture

Two-tier architecture

typically used with 4GL (“Fourth Generation Languages”)i.e. languages for easy development of simple form-based application and reports.

Transaction support through database systemUsed in medium size applications

Client workstation- presentation, requests, GUI -

Database server

Proprietary protocol


ThreeThree--tier Architecture (1)tier Architecture (1)

Application oriented architectureseparation of presentation, application logic and

DB access

e.g. CGI or Servlet application running under control of a web server

Presentatione.g web server

Database serverApplica-tion progs

Browser

http

JDBC /ESQL/ODBC


ThreeThree--tier Architecture (2)tier Architecture (2)

Middle tier: framework for implementing business logic and business objects

Particularly useful with automatic object-relational mapping between database (relational) and programming language (object oriented)

Application serverimplements presentation, session control and business logic (applications)

Database server

e.g. JavaApplet

Data access transparent for application programs

HTML-client

Web-Server


1.5 Technical challenges1.5 Technical challenges

Operational requirement: The DBS should never do anything which destroys the consistency of database and modeled reality (called integrity)

Example:Transfer 100 $ from one account a1 to another one a2. Several steps are required: reading the value of a1, decrease the amount (100 $), write a1, increase the value of a2 by the amount.

Main technical issue:Execution of operations must guarantee correctness properties


Technical challengesTechnical challengesOperational requirement: No interference of operations of different users

Example: Auction system. Two independent bidders A, B read highest bid h, B's bid : h+a , A's bid h+bB's bid is lost even if h+a < h+bA and B are the programs executing the bids for human users


Technical ChallengesTechnical Challenges

Synchronisation of independent DB-users:

How to avoid conflicting read / write access ?concurrent programming

But DB have many resources: each record is a resource –there may be millions (*) of them

Synchronization of thousands of concurrent operations ?

(*) Wal-Mart: 200 Mio transaction / week = 300 TA/sec – 24/7source: The Economist Feb 27,2010


Technical challengesTechnical challengesFail-safe operation

Example: System crash when writing a block with account data on disk. DB must not be corrupted

System failure should not corrupt database stateEfficiency

Hundreds of clients active on the same DB,Hundreds or thousands operations / sec,Response time requirement in interactive environment: < 3 sec

Data securityAccess by unauthorized users might be a disaster


1.6 Lifecycle1.6 Lifecycle

Requirements analysis

Conceptual Design

Schema design- logical (“create tables”)

Schema design- physical (“create access path”)

Loading, administration,tuning, maintenance, reorganization

System analystDB designer

Application programmer

Application programmerDB administrator

DB administrator

Compare: Lifecycle of HW ~3 yearsSoftware ~ 5 years, Data 30 years !?


SummarySummary• Database ≠ Database System• Database: data and metadata (schema)• Data model: high level data definition and data

manipulation language• Relational Data Model (RDM) / SQL• Two- /Three-tier-architecture• Technical requirements

ConcurrencyFault-toleranceIntegrityEfficiency

• Life cycle

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